Aspects of semiconductor technology have focused on increasing the integration of semiconductor devices (e.g., achieving smaller scale devices). The trend toward such small scale devices may require reinforcing inter-element isolation in order to reduce the distances between semiconductor devices.
One method of isolating semiconductor devices electrically is forming a local oxidation (LOCOS) layer. A shortcoming of the LOCOS layer is that a bird's beak may occur at an edge of the field oxide layer because oxygen penetrates into a lateral side of the pad oxide layer from a bottom of the nitride layer used as a mask in the selective oxidation of the silicon substrate. The length of the bird's beak may extend the field oxide layer into an active area. Consequently, the electric characteristics of the transistor may be diminished.
Therefore, there is an increase in demand for a field oxide layer capable of occupying a small area but maintaining good isolation capability. Trench type field oxide layer, particular shallow trench isolation (STI), has been employed. STI may require selectively etching a portion of semiconductor substrate to form a trench for device isolation and filling the trench with an insulating layer.
Meanwhile, in order to obtain small scale devices the width of a trench provided within a substrate is decreased while increasing its depth. Because the decreased width and increased depth of the trench raise an aspect ratio of the trench, step coverage is degraded when depositing a trench insulating layer. An entrance of the trench is blocked before a deep portion of the trench is filled with the insulating layer. This shortcoming results in the reduction of filling the trench with the trench oxide layer.
As illustrated in example FIG. 1, voids (A) can be generated due to the degraded gap-fill capability in filling the trenches with an insulator. If void (A) is generated within a trench oxide layer, it is exposed in the course of planarization of the trench oxide layer to interrupt the planarization. Moreover, if polysilicon deposited for forming an electrode later intrudes void (A), leakage current may be generated which diminishes the characteristics of the semiconductor device.